This invention relates to a solid state relay, and more particularly relates to a novel solid state relay which employs a power MOSFET in the output circuit.
Solid state relays are well known in the art and conventionally employ bipolar semiconductor devices such as thyristors, triacs or power transistors as the power switching element. The use of bipolar switching devices as the output power element of the relay makes it possible to derive control power for the relay from the output circuit when the powwer bipolar devices are conducting. Power MOSFET devices have not been easily utilized in solid state relay circuits because it is difficult to derive control power from the output circuit after the device is switched on. Also, present a-c solid state relay circuits using bipolar devices necessarily produce substantial electromagnetic interferences. Present d-c solid state relay circuits using bipolar devices which derive their power for the relay from the output circuit necessarily have relatively large voltage across the output terminals when turned on, even for relatively small output currents. Also the off switching of the d-c relay is relatively slow.